Most automotive air bag restraint systems, presently in use, use gas generant compositions in which sodium azide is the principal fuel. Because of disadvantages with sodium azide, particularly instability in the presence of metallic impurities and toxicity, which presents a disposal problem for unfired gas generators, there is a desire to develop non-azide gas generant systems and a number of non-azide formulations have been proposed, e.g., U.S. Pat. Nos. 4,369,079 and 5,015,309, the teachings of which are incorporated herein by reference. However, to date, non-azide gas generants have not made significant commercial inroads.
Materials that have been previously proposed for non-azide gas-generants include salts of bitetrazole, aminotetrazole, nitrotriazolone, triazolone, salts of nitrobarbituric acid, salts of nitroorotic acid, nitrouracil, salts of guanidine, and salts of amino-substituted guanidine, such as amino guanidine and triamino guanidine. Disadvantages of these materials include not being commercially available or not being available at a reasonable price and containing hydrogen in their chemical structure. It is advantageous to have fuels that contain little or preferably no hydrogen in their chemical structure. Upon combustion, fuels that contain hydrogen produce water vapor. Water vapor could be disadvantageous to bag performance at cold temperatures due to condensation. Heat capacity of the output gases is also increased with increased water content and potentially results in burns to the vehicle occupant upon inflation of the bag.
U.S. Pat. No. 4,386,979 to Jackson Jr. et al., the teachings of which are incorporated herein by reference, teaches the use of cyanamide, dicyanodiamide (the dimerization product of cyanamide), and salts thereof as fuels in gas generant compositions. While some of the salts of cyanamide and dicyanodiamide are commercially available at a reasonable price and as salts of cyanamide contain no hydrogen, they have the disadvantage of not producing as great a quantity of gas upon combustion as would be desired. Further, they are not produced commercially in the purity that is required. The highest purity of commercial calcium cyanamide is 86 wt %, and the balance 14 wt % CaO renders the material unsuitable as a fuel. Dicyanodiamide has the disadvantage of a high hydrogen content.